For weeks, crews had been first trying to figure out the best method to reach whatever was blocking Bertha from moving forward 60 feet below the surface. They then set to work removing enough water and dirt to reach the mystery object.

Their big break came Thursday.

Yesterday, crews removed enough dirt and water from my excavation chamber to peek inside. Here’s what they saw: http://t.co/GWaPsNyxzA

According to The Seattle Times, officials identified the pipe more specifically as being 115-foot-long “well casing” that was used to measure ground water in 2002 in studies for the Alaskan Way Viaduct replacement project.

“Bertha,” the massive tunnel boring machine, was expected to spend 14 months drilling a two-mile tunnel to replace the 60-year-old Alaskan Way Viaduct. Three delays have since hit the project that began in July. The tunnel will replace the viaduct, a double deck highway along the downtown Seattle waterfront. (AP/Ted S. Warren)

The well site was listed in reference materials provided to bidders as part of the contract specifications, DOT says. “I don’t want people to say WSDOT didn’t know where its own pipe was, because it did,” said DOT spokesman Lars Erickson. However, Chris Dixon, project director for contractor group Seattle Tunnel Partners, said the builders presumed there would be no pipe in the way, because casings are customarily removed after use.

Dixon said the tunnel-machine crew first noticed metal pieces in Bertha’s conveyor system in early December — when Bertha’s rotation actually shoved a segment of pipe through the surface, prompting crews to remove a 55-foot-long piece. However, the machine kept grinding forward just fine, Dixon said, leading STP to have what he called “a false sense of security” that things would be OK.

[…]

Downtown Seattle contains some of the most frequently poked and studied ground on earth, which makes the blockage all the more confounding. Five-foot diameter holes were drilled alongside the tunnel path to install concrete pilings that protect the old viaduct; the contractors have used ground-penetrating radar; and geotechnical experts drilled test holes, which didn’t hit this particular object

Project manager Chris Dixon, left, and Washington Dept. of Transportation deputy administrator Matt Preedy stand in front of a large mural depicting a finished State Route 99 tunnel as they address a news conference Friday, Jan. 3, 2014, in Seattle. The two said that a steel pipe is at least partly to blame for halting the massive tunnel-boring machine beneath downtown Seattle for the highway project. The state Department of Transportation said the 8-inch-diameter pipe, a well casing installed by the department in 2002 to monitor groundwater, was discovered protruding through an opening in the machine’s cutter-head. The tunneling machine, known as “Bertha,” is digging a new path for SR 99, one of the region’s primary north-south arterials. It’s been halted since encountering a mysterious obstruction Dec. 6. (AP/Elaine Thompson)

The Times reported that the officials didn’t alert the public about the pipe until now because the team didn’t initially think it was the primary issue. Many thought it was likely a boulder blocking the $80 million machine.

“Other potential factors include changing soil conditions that may have caused excessive wear of cutting tools, potential objects in front of the cutterhead or objects in the lower portion of the excavation chamber that still aren’t visible,” a statement from the state’sDepartment of Transportation read, according to the Seattle Post-Intelligencer.